Glaucoma is one of the leading causes of blindness in the world. The key to prevention of visual loss from glaucoma is early detection of the disease or its progression and timely treatment. The proposed study will investigate the role of various tests in improving detection of disease progression in advanced glaucoma. Evaluation of the peripheral field of vision (visual field examination) remains the current standard for detection of progression in glaucoma. However, there is a lot of variability or inconsistency in eyes with advanced glaucoma, which could make it difficult to detect worsening of glaucoma with visual fields. The optic nerve demonstrates significant damage in such eyes and hence oftentimes repeat imaging of the optic nerve head is not helpful for detection of change. Therefore, imaging of the central retina (the innermost sensitive tissue lining the inside of the eye), called macula, has been proposed to supplant imaging of the nerve in eyes with severe glaucoma. The macula aids in detailed central vision. Since the macular retinal neural cells are the last ones to be affected in glaucoma, measurement of macular retinal thickness could provide significant information with regard to the course of glaucoma. In the proposed study, glaucoma patients will be tested and followed with various measurements done with newer versions of optical coherence tomography (OCT) imaging and visual field machines. The patients will undergo repeat imaging and visual field testing every 6 months over the course of 5 years. Rates of change will be estimated. We will explore if changes in various outcome measures derived from imaging are correlated with the corresponding visual field changes in glaucoma, and whether the former can be used as an alternative method for detecting simultaneous or subsequent glaucoma progression. The hypothesis for this proposed research is that macular OCT parameters are valid structural measures that can be used especially in advanced disease to follow the course of glaucoma.